Switch mode power supply (SMPS) circuits are power converters that produce a regulated DC output voltage from an unregulated AC or DC input voltage. The Switch mode power supply is a versatile device that can step up or step down the input voltage to produce a regulated output voltage. There are various applications of the SMPS circuits such as the SMPS may be used for step down an unregulated DC input voltage to produce a regulated DC output voltage, which is known as Buck Converter or Step-Down SMPS. The SMPS may be used for step up an unregulated DC input voltage to produce a regulated DC output voltage is known as Boost Converter or Step-Up SMPS. Further, the same SMPS may also be used for producing multiple regulated DC outputs. The SMPS, which uses an AC, input voltage is known as an offline SMPS. The offline SMPS can be of a forward converter type or a flyback-type. The embodiment of this invention is concerned with the forward converter type of SMPS.
The forward converter type offline SMPS circuit may have a half bridge or a full bridge configuration. A half bridge power converter circuit comprises a transformer with a single primary winding coupled to one or more secondary windings and two switching elements such as Field Effect Transistors (FET) or bipolar transistors or insulated gate bipolar transistors (IGBTs) as connected in a half bridge configuration i.e. one out of the two transistors is “on” at a time and thus, the two transistors conduct on alternate half cycles at a time. These two transistors are connected to one end of the primary winding. The other end of the primary winding is connected to the junction of two equal capacity capacitors connected in series, with the DC input voltage Vdc. The junction of the capacitors presents half the DC input voltage to the primary winding end connected to the capacitors, ie Vdc/2.
Further, a full bridge power converter circuit has two additional transistors that are provided in place of the capacitors placed in a half bridge configuration. The four transistors are connected in a bridge configuration, wherein the two diagonally opposite transistors are switched “on” simultaneously during alternate half cycles. As a result, the full DC input voltage is applied across the transformer primary winding i.e. Vdc wherein Vdc is DC input voltage. Thus, the total power yielded in a full bridge configuration is twice that of the half bridge configuration.
The half bridge and the full bridge configurations may be used with an SMPS circuit as discussed above. However, the known SMPS circuits have a major limitation that they can operate only in a limited range of input voltage. This limited varying input voltage operating range for a switch mode power supply forces the consumers of domestic products such as: computers, television receivers, industrial equipments etc. to use additional power conditioning equipment and uninterrupted power supply (UPS). The additional power conditioning equipment adds to cost and additional power consumption. Therefore, there is an utmost need to improve the efficiency and reliability of SMPS in terms of increasing the input voltage range.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.